Make ipaclient.discovery usable from command line
    
    For debugging and testing make it possible to run a simple domain
    discovery from the command line
    
    ```
    $ python3 -m ipaclient.discovery demo1.freeipa.org
    realm    DEMO1.FREEIPA.ORG                      (Discovered from LDAP DNS records in ipa.demo1.freeipa.org)
    domain   demo1.freeipa.org                      (Discovered LDAP SRV records from demo1.freeipa.org)
    basedn   dc=demo1,dc=freeipa,dc=org             (From IPA server ldap://ipa.demo1.freeipa.org:389)
    server   ipa.demo1.freeipa.org                  (Discovered from LDAP DNS records in ipa.demo1.freeipa.org)
    servers  ['ipa.demo1.freeipa.org']
    Success
    $ python3 -m ipaclient.discovery freeipa.org
    realm    None
    domain   None
    basedn   None
    server   None
    servers  []
    NO_LDAP_SERVER
    ```
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>